1. Field of the Invention
This invention relates generally to a method for compressing data and, more particularly, to a method for compressing measurement data that includes grouping common elements in the data, subtracting successive data elements in the groups of common data elements and compressing the subtracted values.
2. Discussion of the Related Art
Modern vehicles include many systems, sub-systems, actuators, sensors, etc. that provide measurement data that is transferred between various systems and sub-systems on the vehicle that allow the vehicle to operate in a desired manner. Typically, the data is transferred between the systems and sub-systems on one or more data busses, sometimes referred to as a controller area network (CAN) data bus. One known vehicle system uses five CAN data busses. When a vehicle is being serviced, tested, developed, etc., the measurement data on the CAN bus is typically transferred to testing equipment and the like separate from the vehicle. It is necessary that this data be stored in a storage device, from which it is then subsequently analyzed. However, a problem exists because the amount of data produced by the vehicle over a certain period of time can be very large, requiring a very large storage device, which increases cost.
Various compression algorithms are known in the art that compress various types of data so that the data can be stored in a memory without using as much storage space as would normally be required. These compression algorithms include WinZip, MP3, etc., all well known to those skilled in the art. A typical compression rate for known lossless compression algorithms is between two and four, meaning that the average reduction of the storage space required for the digital data is reduced by a factor of two to four from the original data.
Further, not only is the amount of storage space required in various applications significant, but the transfer time for transmitting the data from the storage device to the testing equipment is also significant. Thus, it typically takes a large amount of time to download the data from the storage device, also increasing cost.
The well known MP3 compression algorithm has a relatively high compression rate, typically between 10 and 12 depending on the bit rate used. However, because it is used for audio compression, the algorithm provides for a certain amount of loss as a result of the compression process where the restored audio or music will not be of the same quality as the original audio or music. For audio compression, such a lossy compression process is typically sufficient because the difference in music quality is not discernable to human ears. However, for measurement data compression, such losses would not be acceptable.